How effective is ‘greening’ of urban areas in reducing human exposure to ground-level ozone concentrations, UV exposure and the ‘urban heat island effect’? An updated systematic review

Table 1 Summary counts for study validity grades

Study validity grade	Low risk of bias	Moderate risk of bias	High risk of bias	Very high risk of bias
Experimental	5	14	41	1
Observational	–	44	162	45
Total	5	58	203	46